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Message-Id: <DB5B4E8A-3CE9-4F15-A52F-BA75E9BDA4FF@gmail.com>
Date: Wed, 13 Aug 2025 11:38:40 +0800
From: wang lian <lianux.mm@...il.com>
To: Zi Yan <ziy@...dia.com>
Cc: Wei Yang <richard.weiyang@...il.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
David Hildenbrand <david@...hat.com>,
linux-mm@...ck.org,
Andrew Morton <akpm@...ux-foundation.org>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Nico Pache <npache@...hat.com>,
Ryan Roberts <ryan.roberts@....com>,
Dev Jain <dev.jain@....com>,
Barry Song <baohua@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>,
Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Shuah Khan <shuah@...nel.org>,
linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 2/4] selftests/mm: add check_folio_orders() helper.
> On Aug 12, 2025, at 23:55, Zi Yan <ziy@...dia.com> wrote:
>
> The helper gathers an folio order statistics of folios within a virtual
> address range and checks it against a given order list. It aims to provide
> a more precise folio order check instead of just checking the existence of
> PMD folios.
>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
> .../selftests/mm/split_huge_page_test.c | 4 +-
> tools/testing/selftests/mm/vm_util.c | 173 ++++++++++++++++++
> tools/testing/selftests/mm/vm_util.h | 7 +
> 3 files changed, 181 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> index 5d07b0b89226..63ac82f0b9e0 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -34,8 +34,6 @@ uint64_t pmd_pagesize;
> #define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
> #define PATH_FMT "%s,0x%lx,0x%lx,%d"
>
> -#define PFN_MASK ((1UL<<55)-1)
> -#define KPF_THP (1UL<<22)
> #define GET_ORDER(nr_pages) (31 - __builtin_clz(nr_pages))
>
> int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
> @@ -49,7 +47,7 @@ int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>
> if (kpageflags_file) {
> pread(kpageflags_file, &page_flags, sizeof(page_flags),
> - (paddr & PFN_MASK) * sizeof(page_flags));
> + PAGEMAP_PFN(paddr) * sizeof(page_flags));
>
> return !!(page_flags & KPF_THP);
> }
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 6a239aa413e2..4d952d1bc96d 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -338,6 +338,179 @@ int detect_hugetlb_page_sizes(size_t sizes[], int max)
> return count;
> }
>
> +static int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
> +{
> + size_t count;
> +
> + count = pread(kpageflags_fd, flags, sizeof(*flags),
> + pfn * sizeof(*flags));
> +
> + if (count != sizeof(*flags))
> + return -1;
> +
> + return 0;
> +}
> +
> +static int get_page_flags(char *vaddr, int pagemap_fd, int kpageflags_fd,
> + uint64_t *flags)
> +{
> + unsigned long pfn;
> +
> + pfn = pagemap_get_pfn(pagemap_fd, vaddr);
> + /*
> + * Treat non-present page as a page without any flag, so that
> + * gather_folio_orders() just record the current folio order.
> + */
> + if (pfn == -1UL) {
> + *flags = 0;
> + return 1;
> + }
> +
> + if (get_pfn_flags(pfn, kpageflags_fd, flags))
> + return -1;
> +
> + return 0;
> +}
> +
> +/*
> + * gather_folio_orders - scan through [vaddr_start, len) and record folio orders
> + * @vaddr_start: start vaddr
> + * @len: range length
> + * @pagemap_fd: file descriptor to /proc/<pid>/pagemap
> + * @kpageflags_fd: file descriptor to /proc/kpageflags
> + * @orders: output folio order array
> + * @nr_orders: folio order array size
> + *
> + * gather_folio_orders() scan through [vaddr_start, len) and check all folios
> + * within the range and record their orders. All order-0 pages will be recorded.
> + * Non-present vaddr is skipped.
> + *
> + *
> + * Return: 0 - no error, -1 - unhandled cases
> + */
> +static int gather_folio_orders(char *vaddr_start, size_t len,
> + int pagemap_fd, int kpageflags_fd,
> + int orders[], int nr_orders)
> +{
> + uint64_t page_flags = 0;
> + int cur_order = -1;
> + char *vaddr;
> +
> + if (!pagemap_fd || !kpageflags_fd)
> + return -1;
> + if (nr_orders <= 0)
> + return -1;
> +
> + for (vaddr = vaddr_start; vaddr < vaddr_start + len;) {
> + char *next_folio_vaddr;
> + int status;
> +
> + status = get_page_flags(vaddr, pagemap_fd, kpageflags_fd,
> + &page_flags);
> + if (status < 0)
> + return -1;
> +
> + /* skip non present vaddr */
> + if (status == 1) {
> + vaddr += psize();
> + continue;
> + }
> +
> + /* all order-0 pages with possible false postive (non folio) */
> + if (!(page_flags & (KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))) {
> + orders[0]++;
> + vaddr += psize();
> + continue;
> + }
> +
> + /* skip non thp compound pages */
> + if (!(page_flags & KPF_THP)) {
> + vaddr += psize();
> + continue;
> + }
> +
> + /* vpn points to part of a THP at this point */
> + if (page_flags & KPF_COMPOUND_HEAD)
> + cur_order = 1;
> + else {
> + /* not a head nor a tail in a THP? */
> + if (!(page_flags & KPF_COMPOUND_TAIL))
> + return -1;
> +
> + vaddr += psize();
> + continue;
> + }
> +
> + next_folio_vaddr = vaddr + (1UL << (cur_order + pshift()));
> +
> + if (next_folio_vaddr >= vaddr_start + len)
> + break;
> +
> + while ((status = get_page_flags(next_folio_vaddr, pagemap_fd,
> + kpageflags_fd,
> + &page_flags)) >= 0) {
> + /*
> + * non present vaddr, next compound head page, or
> + * order-0 page
> + */
> + if (status == 1 ||
> + (page_flags & KPF_COMPOUND_HEAD) ||
> + !(page_flags & (KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))) {
> + if (cur_order < nr_orders) {
> + orders[cur_order]++;
> + cur_order = -1;
> + vaddr = next_folio_vaddr;
> + }
> + break;
> + }
> +
> + /* not a head nor a tail in a THP? */
> + if (!(page_flags & KPF_COMPOUND_TAIL))
> + return -1;
> +
> + cur_order++;
> + next_folio_vaddr = vaddr + (1UL << (cur_order + pshift()));
> + }
> +
> + if (status < 0)
> + return status;
> + }
> + if (cur_order > 0 && cur_order < nr_orders)
> + orders[cur_order]++;
> + return 0;
> +}
> +
> +int check_folio_orders(char *vaddr_start, size_t len, int pagemap_fd,
> + int kpageflags_fd, int orders[], int nr_orders)
> +{
> + int *vaddr_orders;
> + int status;
> + int i;
> +
> + vaddr_orders = (int *)malloc(sizeof(int) * nr_orders);
> +
> + if (!vaddr_orders)
> + ksft_exit_fail_msg("Cannot allocate memory for vaddr_orders");
> +
> + memset(vaddr_orders, 0, sizeof(int) * nr_orders);
> + status = gather_folio_orders(vaddr_start, len, pagemap_fd,
> + kpageflags_fd, vaddr_orders, nr_orders);
> + if (status)
> + goto out;
> +
> + status = 0;
Nit.
It seems redundant.
Would you consider removing it for a bit more conciseness?
This doesn't block my approval, of course.
Reviewed-by: wang lian <lianux.mm@...il.com>
> + for (i = 0; i < nr_orders; i++)
> + if (vaddr_orders[i] != orders[i]) {
> + ksft_print_msg("order %d: expected: %d got %d\n", i,
> + orders[i], vaddr_orders[i]);
> + status = -1;
> + }
> +
> +out:
> + free(vaddr_orders);
> + return status;
> +}
> +
> /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
> int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
> bool miss, bool wp, bool minor, uint64_t *ioctls)
> diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
> index 1843ad48d32b..02e3f1e7065b 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -18,6 +18,11 @@
> #define PM_SWAP BIT_ULL(62)
> #define PM_PRESENT BIT_ULL(63)
>
> +#define KPF_COMPOUND_HEAD BIT_ULL(15)
> +#define KPF_COMPOUND_TAIL BIT_ULL(16)
> +#define KPF_THP BIT_ULL(22)
> +
> +
> /*
> * Ignore the checkpatch warning, we must read from x but don't want to do
> * anything with it in order to trigger a read page fault. We therefore must use
> @@ -85,6 +90,8 @@ bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size);
> int64_t allocate_transhuge(void *ptr, int pagemap_fd);
> unsigned long default_huge_page_size(void);
> int detect_hugetlb_page_sizes(size_t sizes[], int max);
> +int check_folio_orders(char *vaddr_start, size_t len, int pagemap_file,
> + int kpageflags_file, int orders[], int nr_orders);
>
> int uffd_register(int uffd, void *addr, uint64_t len,
> bool miss, bool wp, bool minor);
> --
> 2.47.2
>
Best regards,
wang lian
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